The present invention relates to a conveyance system for use in microwave processing of products such as, for example, the sterilization and/or cooking of food articles, and in particular to a constraint mechanism for holding conveyed items in place providing minimal mechanical interference with the microwave energy applied to improve the uniformity of results in such systems.
The processing of products with microwave energy, such as needed for cooking, sterilization, and similar operations, involves placing the product within some sort of enclosed waveguide applicator for a time. Many different approaches have been tried to improve the uniformity of results in such systems. These usually involve carefully designing the shape of the waveguide applicator.
For large scale, high volume, commercial applications, it is typically desirable to process as many items in as short a time as possible. In these situations, it is common to use a continuous conveyor to transport items through the applicator. Conveyor belts made of materials that are suitable for use in such environments are well known. For example, materials such as Teflon™, Kevlar™ or fiberglass have been used for conveyors in microwave ovens.
In addition to ensuring that the microwave applicator is of proper dimension, it is also important to ensure that the position of the product with respect to the waveguide is carefully controlled. There is no advantage to having a precisely dimensioned microwave applicator if consistent positioning of the product within the applicator cannot be assured as it travels through the applicator. If the product moves up and down or from side to side while being conveyed through the applicator, uneven results will occur.
One manner of constraining conveyed packaged items is described in a co-pending U.S. patent application Ser. No. 11/335,837, filed Jan. 19, 2006 (U.S. Patent Publication No. 2006/0231150) entitled “Product Guidance System for Continuous Conveyor Microwave Oven”, which is assigned to The Ferrite Company, Inc. The approach in that system was to use a series of fixed wire guides located adjacent the conveyor.
Many different approaches have been attempted, all of which utilize a mechanical structure that spans the microwave exposure area with some form of traditional conveyor belt or other transport mechanisms. These methods introduce significant mechanical structures into the microwave heating area (ie. Kevlar mesh belts, plastic link belts or other plastic cradle structures) causing interference with the microwave field and loss of uniformity in heating. The benefits of a carefully designed waveguide applicators are diminished by undesirable interaction with the microwave energy created by the mechanical structures.